Accordion-shaped welded metal bellows having sealing properties and flexibility can be compressed until the bellows plates closely contact one another, and therefore are used for sealing moving members of a variety of instruments. For example, a welded metal bellows used for sealing a gate valve with which an opening in a vacuum processing chamber used in a manufacturing step of a semiconductor-manufacturing device can be opened and closed in an airtight manner is used to seal off a vacuum side and an atmosphere side. As shown in FIG. 4, individual bellows plates 50 are connected by being welded on the inside-diameter side and the outside-diameter side into a bellows shape, and the bellows is repeatedly extended and contracted over a period of several million strokes at a high speed (hereinafter referred to as “Prior Art 1”). A problem of this type of bellows is that when a foreign matter present in the vacuum atmosphere, such as a metal particle 51, enters between the bellows plates 50 in the manner shown in FIG. 4(a), the bellows plates 50 undergo bending deformation during contraction according to the lever principle, as shown by the dashed and dotted lines; cracks appear in the bellows plate 50 near the metal particle 51 during repeated extension and contraction, as shown in FIG. 4(b); and the bellows eventually fails, resulting in a shorter-than-designed service life and making the bellows unusable.
A variety of welded metal bellows have been proposed in the past. For example, a welded metal bellows 60 such as the one shown in FIG. 5 is known as one having excellent corrosion resistance and operating spring properties (hereinafter referred to as “Prior Art 2”; for example, see Patent Document 1). The bellows plates 61 from which the accordion-structured structure of the bellows 60 according to Prior Art 2 is configured are shaped in two layers in which austenite stainless steel plates 62 are arranged to the sealing fluid side, spring steel plates 63 are arranged to the non-sealing fluid side, and the plates are joined together by welding on the inside-diameter side and the outside-diameter side.
Additionally, a welded metal bellows 70 such as the one shown in FIG. 6 is known as one that provides a bellows capable of withstanding great pressure without sacrificing the flexibility of the bellows (hereinafter referred to as “Prior Art 3”; for example, see Patent Document 1). The bellows plates 71 from which the accordion-structured structure of the bellows 70 according to Prior Art 3 is configured are shaped in two layers in which two circular plates 72, 73 of uniform thickness are joined by welding on the inside-diameter side and the outside-diameter side. The plates are configured so that air holes 74 are provided to the circular plate 72 on the atmospheric side, and there are no gas pockets present between the circular plates 72, 73.
However, Prior Art 2 shown in FIG. 5 provides a welded bellows having excellent corrosion resistance and operating spring properties and has no countermeasures in place against repeated bending deformation due to the ingress of foreign matter. A resulting problem is that the two bellows plates 62, 62 undergo repeated bending deformation when foreign matter 64 enters between the bellows plates 62, 62 on the sealing fluid side, and the two bellows plates fail one after the other or both at the same time.
Prior Art 3 shown in FIG. 6 provides a bellows capable of withstanding significant pressure without sacrificing flexibility. Air holes 74 are formed in the bellows plates 72 on the atmospheric side. A resulting problem is that the bellows can no longer maintain sealing action when the bellows plates 73 on the side opposite from the atmospheric side fail as a result of repeated bending deformation due to the ingress of foreign matter, and the same service life is ultimately obtained as in the case of single bellows plates.